OSCILLATOR DESIGN Oscillator circuits are used for generating the periodic signals that are needed in various applications. These circuits convert a part of dc power into the periodic output and do not require a periodic signal as input. This chapter begins with the basic principle of sinusoidal oscillator circuits. Several transistor circuits are subsequently analyzed in order to establish their design procedures. Ceramic resonant circuits are frequently used to generate reference signals while the voltage-controlled oscillators are important in modern frequency synthesizer design using the phase-lock loop. . | Radio-Frequency and Microwave Communication Circuits Analysis and Design Devendra K. Misra Copyright 2001 John Wiley Sons Inc. ISBNs 0-471-41253-8 Hardback 0-471-22435-9 Electronic 11 OSCILLATOR DESIGN Oscillator circuits are used for generating the periodic signals that are needed in various applications. These circuits convert a part of de power into the periodic output and do not require a periodic signal as input. This chapter begins with the basic principle of sinusoidal oscillator circuits. Several transistor circuits are subsequently analyzed in order to establish their design procedures. Ceramic resonant circuits are frequently used to generate reference signals while the voltage-controlled oscillators are important in modem frequency synthesizer design using the phase-lock loop. Fundamentals of these circuits are discussed in this chapter. Diode-oscillators used at microwave frequencies are also summarized. The chapter ends with a description of the microwave transistor circuits using S- parameters. FEEDBACK AND BASIC CONCEPTS Solid-state oscillators use a diode or a transistor in conjunction with the passive circuit to produce sinusoidal steady-state signals. Transients or electrical noise triggers oscillations initially. A properly designed circuit sustains these oscillations subsequently. This process requires a nonlinear active device. In addition since the device is producing RF power it must have a negative resistance. The basic principle of an oscillator circuit can be explained via a linear feedback system as illustrated in Figure . Assume that a part of output F is fed back to the system along with input signal X. As indicated the transfer function of the forward- 449 450 OSCILLATOR DESIGN Figure A simple feedback system. connected subsystem is A while the feedback path has a subsystem with its transfer function as p. Therefore Y A X pY Closed-loop gain T generally called the transfer function of this system is found from this .
